Polybutylene Terephthalate (PBT)
Polybutylene terephthalate (PBT), a strong and highly crystalline synthetic resin, produced by the polymerization of butanediol and terephthalic acid. PBT is similar in structure to polyethylene terephthalate (PET) – the difference being in the number of methylene (CH2) groups present in the repeating units of the polymer molecules. The mechanical properties of the two materials are also similar.
However, PBT has a lower melting point (223 °C [433 °F]) than PET (255 °C [491 °F]), so it can be processed at lower temperatures. This property, combined with its excellent flow when molten and its rapid crystallization upon cooling, makes PBT highly suitable for injection-molding into solid parts. Either unmodified or reinforced with glass fibers or mineral fillers, it is used in numerous applications, especially electrical and small machine parts, owing to its excellent electrical resistance, surface finish, and toughness.
PBT lends rigidity and thermoplastic properties to a synthetic rubber known as copolyester elastomer.
|Acids – dilute||Good|
|Greases and Oils||Good|
|Dielectric constant @1kHz||3.2|
|Dielectric strength ( kV.mm-1)||20|
|Dissipation factor @ 1kHz||0.002|
|Volume resistivity ( Ohm.cm )||1015|
|Elongation at break ( % )||250|
|Hardness – Rockwell||M70|
|Izod impact strength ( J.m-1 )||60|
|Tensile modulus ( GPa )||2|
|Tensile strength ( MPa )||50|
|Density ( g.cm-3 )||1.31|
|Limiting oxygen index ( % )||25|
|Water absorption – over 24 hours ( % )||0.1|
|Heat-deflection temperature – 0.45MPa (°C )||150|
|Heat-deflection temperature – 1.8MPa (°C )||60|
|Upper working temperature (°C )||120|